The present invention relates to scaffolding equipment, and more particularly to a pump jack adapted for traveling up and down a pole.
While working on elevated surfaces on a building it is necessary to erect a scaffolding in order to permit workers to stand at the elevation above the ground surface. Typically, in connection with the installation of siding on the exterior of a building, it has been customary to utilize for this purpose pump jacks which ride on vertical poles and support a platform on which the workers can stand. The worker stands on the platform and manipulates the pump jack by using his foot to pump the jack and thus raise it in a stepwise manner along the pole. To lower the pump jack, he depresses a release pedal and using a hand lever he rolls the pump jack down the pole.
The pump jacks of the foregoing type typically include a frame and an upper and lower shackle supported by the frame. The pump jack further includes a foot operated pump arm pivotally connected to the frame and adapted to operate the shackles in alternating relationship so as to cause the upper and lower shackles to alternately grip the pole as the weight of the worker shifts from the platform to the pump arm and then back. When the upper shackle grips the pole, depressing the pump arm steps up the frame relative to the pole. Then the weight of the worker standing on the scaffolding staging shifts so that the lower shackle grips the pole while the pump jack remains in place on the pole. However in lifting up the pump arm back again, the upper shackle moves up along the pole to a next position on the pole. In such manner each non-gripping shackle steps up the pole while the opposite shackle grips the pole. In order to ride the pump jack down the pole, the lower shackle is released from gripping the pole and the upper shackle is rolled down the pole by means of a handle provided on the pump jack.
Pump jacks of the type under consideration are disclosed in applicant's Pat. Nos. 4,382,488; 4,463,828; and 4,597,471.
Upper shackles in conventional pump jacks are formed of two substantially U-shaped members, pivotable with respect to each other. One U-shaped member is a yoke member and has two gripping rollers for engaging onto a pump jack pole for climbing up and down the pole. The second is a linkage member, pivotable on the pump arm of the pump jack and is biased relative to the yoke member by tension springs connected between the two members. The springs ensure that the upper shackle is tightened on the pole and also aids in releasing the yoke member from gripping onto the pole when the upper shackle is being stepped up along the pole. Because of the springs, however, in depressing the pump arm to step up the pump jack frame along the pole, the worker must not only exert a force to raise the frame, but must also exert a force to overcome the force of the springs. As a result such pumping makes it hard on the operator's foot.
The lower shackles of conventional pump jacks are also formed by two substantially U-shaped members which are pivoted together and are biased with respect to one another by tension springs. Lower shackles are typically used for temporarily gripping the pole while the upper shackle steps up along the pole. However, when the upper shackle is rolling down the pole, the lower shackle must be pushed forward away from the pole to avoid gripping of the pole. With the two U-shaped members, the yoke member is pivoted to the U-shaped linkage member and the linkage member is then pivotally secured to the pump jack frame in a scissor action. As a result, when pushing forward the lower shackle to release it from the pole, pressing forward on the yoke member requires a considerable effort because a great amount of leverage is required to disengage and retain the lower shackle from the pole. Additionally, because of this double U-member arrangement, the spacing of the front of the yoke member from the pole is minimal and often the yoke member may accidentally catch and regrip the pole thereby causing a problem in rolling down the pump jack along the pole.
Furthermore, with the double U-member arrangement, when releasing the lower shackle, the shackle moves in an arcuate path. This also causes the pump jack frame to arcuate whereby a momentary sensation of the jack dropping downward has resulted. This causes fear to the inexperienced user and even to the experienced worker operating at great heights it causes great concern.
Accordingly, while conventional pump jacks for industrial use have been found satisfactory, additional modifications are warranted to further improve the use of such equipment.